1. Field of the Invention
The present invention relates to methods and devices that can be used alone or in combination to prevent extrusion failure of o-ring seal assemblies that are employed in high temperature and high pressure environments, such as the type of environment found down hole in a gas or oil well. Each of these methods and devices functions to reduce the gap between the plug and its associated channel member where the o-ring is located so that the when the o-ring becomes more pliable under high pressure and high temperature conditions, the gap is sufficiently narrowed to prevent the o-ring from extruding through the gap and thus preventing the failure of the o-ring.
2. Description of the Related Art
Extrusion failure of O-rings in o-ring assemblies occurs when the contained pressurized fluid forces the o-ring to extrude through the gap that exists between the adjoining parts of the seal assemblies, specifically between the plug and the chamber member. Common o-ring materials extrude more readily at very high temperatures because the rubber based material becomes weaker when very hot. Under high pressure and high temperature, an o-ring becomes more pliable and tends to flow or extrude via the gap. When this happens, the o-ring fails and the seal is lost.
Because the types of O-rings employed at high temperature and high pressure are very expensive, by reducing the failure of o-ring assemblies, the present invention reduces the costs associated with replacing the o-ring. These costs including the actual cost of the replacement o-ring and all of the other costs associated with replacing the o-ring. The other cost associated with replacing the o-ring can amount to much more that the cost of the o-ring itself. Depending on the application where the o-ring seal assembly is employed, these other replacement costs can include lost production time, cost of equipment needed to pull the failed assembly out of the production well, cost of manpower required to pull the failed assembly, etc.
Very high pressures increase the probability of extrusion failure of the o-ring for two reasons: the driving force or pressure to extrude the material is greater, and the gap between the adjoining parts increases at very high pressures in commonly used o-ring seal assemblies. In commonly used o-ring seal assemblies, as pressure in the vessel increases, the inside diameter of the vessel or chamber member increases. However, as pressure in the vessel increases, the outside diameter of the plug remains nearly constant. This results in an increasing gap between the plug and chamber member which can lead to o-ring extrusion failure. To reduce the probability of extrusion failure, it is desirable to maintain gap dimensions between the plug and chamber member near zero at very high temperatures and pressures.
Current methods of maintaining gap dimensions at near zero have generally focused on filling the gap with a non-metallic backup ring, such as Teflon, in order to try to place a barrier between the o-ring and the gap for the purpose of preventing the o-ring from extruding around the backup ring and then through the gap. None of the current methods have addressed the problem by utilizing the increasing temperature and pressure to assist in reducing the gap.
The present invention addresses this problem by employing three different methods and devices, each of which can be used alone or in combination, to reduce the gap between the plug and chamber member at high temperature and pressure and thereby prevent o-ring failure in o-ring seal assemblies.